Semiconductors based on Group III-V compounds such as GaN and AlGaN are widely used for optoelectronics, electronic devices and the like owing to many benefits of having a wide and easily controllable bandgap energy.
Light emitting devices such as light emitting diodes or laser diodes using Group III-V or II-IV compound semiconductor materials can render a variety of colors such as red, green, blue and UV light through development of thin film growth techniques and device materials, realize white light with superior efficiency by using a fluorescent material or combining colors and have advantages such as low power consumption, semi-permanent lifespan, rapid response rate, safety and environmental friendliness, as compared to conventional light sources such as fluorescent lamps and incandescent lamps.
Accordingly, these light emitting devices are increasingly applied to transmission modules of optical communication units, light emitting diode backlights as a replacement for cold cathode fluorescent lamps (CCFLs) constituting backlights of liquid crystal display (LCD) devices, and lighting apparatuses using white light emitting diodes as a replacement for fluorescent lamps or incandescent lamps, headlights for vehicles and traffic lights.
A light emitting device may use GaN as a nitride-based semiconductor for a light emitting structure and the light emitting structure may include a first conductivity-type semiconductor layer, an active layer and a second conductivity-type semiconductor layer.
The nitride-based semiconductor layer grown on a sapphire substrate, which is an insulating substrate, may have defects deteriorating crystallinity such as dislocation, melt-back, cracks, pits and surface morphology since the substrate and the light emitting structure include different materials and there are thus lattice mismatch and great differences in thermal expansion coefficients therebetween.
In order to prevent dislocation among these problems, epitaxial lateral over-growth (ELOG) or Pendeo growth methods have been suggested.
FIGS. 1 and 2 show growth of a conventional nitride-based semiconductor.
FIG. 1 shows an ELOG growth method. Masks are formed with silicon oxide (SiO2) in the center of a nitride-based semiconductor (GaN) grown on a substrate, and the nitride-based semiconductor grown in a region between masks is grown vertically as well as horizontally above the masks, thereby removing defects in the region on the mask.
FIG. 2 shows a Pendeo growth method. A substrate is etched to form grooves and a nitride-based semiconductor layer is grown on the substrate in regions where the grooves are not formed. In this case, the nitride-based semiconductor grown in a part of the substrate is grown vertically and horizontally, so that the nitride-based semiconductor layer can be formed over the entire top surface of the substrate.
However, conventional nitride-based semiconductor growth methods have the following problems.
The ELOG method may lead to tilt resulting from friction between silicon oxide used as a mask and GaN, thus causing dislocation. In addition, it takes a prolonged time for the nitride-based semiconductor to horizontally grow on the mask as well as over the entire region above the mask.
The Pendeo method requires etching to the sapphire substrate. In this regard, process time is lengthened and it is difficult to etch an accurate pattern on the sapphire substrate.